JP2008309998A - Tilt lens system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tilt lens system which is set to use AF and AE not only when it is in an ordinary using state but also when it is titled so as to easily perform operation for tilt and shift photography, and has very little aberration fluctuation, and an imaging apparatus equipped with the tilt lens system. <P>SOLUTION: The tilt lens system 2A, where a tilt lens group 290 capable of tilting an optical axis a2 to a main optical axis a1 shared by a focus lens group 210 movable when focusing and the center of a diaphragm S and having negative refractive power is arranged nearer to an image side than the focus lens group and the diaphragm, satisfies conditional expressions (1) 1.3<βt<1.7 and (2) 0<P<H1, provided that βt: lateral magnification of the tilt lens group when the optical axis is not tilted, P: a distance from the surface of the tilt lens group nearest to an object side to the center of tilting when the optical axis is tilted, and H1: a distance from the surface of the tilt lens group nearest to the object side to a first principal point. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel tilt lens system and an imaging apparatus. Specifically, in video cameras, digital cameras, and single-lens reflex digital cameras or film cameras, not only the subject placed in parallel with the imaging surface but also the imaging surface without impairing the autofocus function and the exposure measurement function. The present invention relates to a tilt lens system having a so-called tilt tilt function that can also focus on a tilted subject and an imaging apparatus including the tilt lens system.

  In a general imaging apparatus, the optical axis of the lens is arranged so as to be orthogonal to the imaging surface made of an imaging element or film at the center. For this reason, for example, when a high building is photographed at an elevation angle, the upper part of the building is narrowed due to perspective. Also, it is impossible to focus on the entire subject surface that is tilted with respect to the imaging surface, and the depth of field is increased by using a small aperture to capture the image as if it is in focus. It will be. For the purpose of eliminating such inconveniences in photographing, it is called “tilting” that the positional relationship between the optical axis of the lens and the imaging surface is translated or tilted.

  In order to correct perspective, such as elevation shooting, the main plane of the subject and the lens and the imaging plane are arranged and held in parallel, and the shooting range is determined. So-called framing is the so-called framing where the optical axis hits the imaging plane. This is done by shifting the position. This tilting operation is called shift, rise, fall, etc. depending on the direction of shifting, but in this specification, all are called shifting regardless of the shifting direction.

  Next, in order to focus on a plane that is tilted with respect to the imaging surface, the tilt that breaks the parallelism between the main plane of the lens and the imaging surface is called a swing or tilt, etc. Regardless of what you call it tilt.

  As an imaging apparatus capable of tilting as described above, there are known a view camera and a camera called an assembly dark box in which the lens board and the imaging surface are connected with a bellows and the mutual positional relationship can be freely operated. However, this type of camera has to be tilted and focused while observing an inverted image on the focusing screen, and is a special camera that is extremely difficult to use.

  As an interchangeable lens for a single-lens reflex camera that is widely used, there is a lens that can use a shift and a tilt function, which makes the tilt operation much easier to use than a view camera. However, when tilting with these lenses, it may be used outside the image height of the normal screen size, so the lens design is required to cover a wider image circle with the same image quality as a normal interchangeable lens. It is done. One example is disclosed in Patent Document 1.

  By the way, in recent years, most imaging devices have shifted from film to digital cameras using imaging devices, and even when filmed with film, it has become common to convert digital information with a scanner and output it to various media. I came. When this digital image information is output as a print, a printed document or a computer image, it is often processed by image editing processing software called retouching software. The retouching software can adjust the hue, brightness, contrast, sharpness, etc., and perform trimming and image composition. Many of these functions have perspective correction. . This is a normal camera when shooting, for example, taking a picture of the building at an elevation angle and copying it to the upper constriction, transforming the image into a trapezoidal shape so that the width of the upper part of the building is widened by digital signal processing, and then rectangular By trimming, the effect is as if it was shot with shift tilt. Since the image is deformed into a trapezoidal shape, the upper part of the stretched screen is considered to have a lower resolution. However, with a single-lens reflex digital camera or data read from a film with a high pixel pitch, it is originally sufficient. Since it has a resolution, even if there is a slight decrease in resolution, it does not have to be a problem. In this way, if retouching software that has become popular in recent years is used, it is no longer necessary to use a shift tilt that is difficult to use during shooting.

  Also, as one of the effects of tilt aori, when shooting a landscape at infinity, intentionally focusing on a part of the screen and blurring the other parts, the real landscape, as if the diorama was close There are shooting methods that show the effect of shooting from However, this is also possible with retouching software, and it is possible to create an image as if it was blurred with a tilted tilt by intentionally blurring a part of the image that is in focus.

  Therefore, an effect that cannot be achieved with retouching software, and that can only be achieved with a tilt lens, is that when the subject plane, the main plane of the lens, and the imaging surface intersect at a single ridgeline, the subject plane is in focus. Has been limited to satisfying so-called Shine-Pluff's law.

  As the prior art that enables tilt tilt, those described in Patent Documents 2 and 3 are known.

JP 2000-292689 A JP-A-4-243212 JP-A-4-243207

  In commonly used imaging devices, it is common sense that AF (autofocus) and AE (automatic exposure) functions. Then, when looking at the interchangeable lens with tilt function again, some are manual focus instead of AF, and others are fully automatic apertures, so when the tilt function is not used, AE works correctly, When tilting, the center of the exit pupil deviates from the center of the screen, the exit pupil falls with the tilt, the positional relationship between the exit pupil, the Fresnel lens on the focusing screen, and the photometric element collapses, and AE does not work correctly. There is a case. In the manual focus system described above, the fully automatic aperture is a mechanical interlocking mechanism, so it is extremely difficult to mechanically interlock when the aperture blades are displaced from the optical axis due to tilting or fall with the optical axis. It seems that this is the case, and a preset-type aperture is used in which the user manually performs the aperture operation, and even when the tilt is not performed, the AE malfunctions except when the aperture is open.

  In this way, the interchangeable lens with tilt function can obtain a shooting effect that is not possible with other lenses, but it cannot be used for normal shooting, and it is difficult to use a preset aperture that is difficult to use. Have The best way to perform tilt and tilt is to repeat manual operations such as focusing with manual focus and then tilting according to the tilt of the subject. The focus and tilt angle must be adjusted to make it extremely difficult to use.

  In those described in Patent Documents 2 and 3, in a lens system that tilts a part of the lens system to obtain the tilt effect, the image on the optical axis before tilting is centered even after tilting. The paraxial optical consideration for not moving the lens is shown, and the problem when the partial lens group is tilted is the movement of the central image. However, the biggest problem when tilting the partial lens group is performance degradation caused by the loss of aberration correction balance when continuously changing from the coaxial optical system to the extreme decentered optical system. Clearly, no solution or numerical example is shown for the problem of always maintaining the imaging performance as a whole even if the balance of aberration correction changes. Therefore, the object of providing a tilt lens system for practical use has not been achieved.

  The present invention does not adopt the shift tilt function that can be substituted by retouching software as described above, and tilts only a part of the lens groups while always arranging the components related to AF and AE on the main optical axis. Able to enable shooting that satisfies Scheinpf's law, and enables AF and AE to be used not only during normal use but also when tilted, making tilt-and-ori shooting operations easy. It is an object of the present invention to provide a tilt lens system with very little fluctuation and an image pickup apparatus including the tilt lens system.

A tilt lens system according to an embodiment of the present invention includes a tilt lens group that can tilt the optical axis with respect to a main optical axis shared by a focus lens group that is movable during focusing and the center of the stop, and has negative refractive power. Are arranged on the image side of the focus lens group and the stop, and the following conditional expressions (1) and (2) are satisfied.
(1) 1.3 <βt <1.7
(2) 0 <P <H1
However,
βt: Lateral magnification of the tilt lens group when the optical axis is not tilted P: Distance from the most object side surface of the tilt lens group to the tilt center when the optical axis is tilted H1: From the most object side surface of the tilt lens group The distance to the first principal point.

  An imaging apparatus according to an embodiment of the present invention includes a tilt lens system according to the present invention and an image sensor that converts a subject image formed by the tilt lens system into an electrical signal.

  In the present invention, by tilting only a part of the lens units, it is possible to perform shooting that satisfies the Shine-Pluff's law, and AF and AE are used not only during normal use but also when tilted. This makes it possible to easily perform tilt-aori shooting.

  The best mode for carrying out the tilt lens system and the imaging apparatus of the present invention will be described below.

  First, the tilt lens system of the present invention will be described.

The tilt lens system according to the present invention includes a tilt lens group that can tilt the optical axis and has a negative refractive power with respect to the main optical axis shared by the focus lens group that is movable during focusing and the center of the aperture. Arranged on the image side from the stop, the following conditional expressions (1) and (2) are satisfied.
(1) 1.3 <βt <1.7
(2) 0 <P <H1
However,
βt: Lateral magnification of the tilt lens group when the optical axis is not tilted P: Distance from the most object side surface of the tilt lens group to the tilt center when the optical axis is tilted H1: From the most object side surface of the tilt lens group The distance to the first principal point.

  Therefore, in the present invention, by tilting only a part of the lens groups, it is possible to perform photographing that satisfies the Shine-Pruff's law, and not only in a normal use state but also when tilting, AF and AE. Can be used, and the tilt aori shooting operation can be easily performed.

  FIG. 1 is a diagram for explaining the basic paraxial refractive power arrangement and effects of an imaging apparatus using the tilt lens system of the present invention.

  The image pickup apparatus 1 includes a tilt lens system 2 and an image pickup surface 3. The tilt lens system 2 has a master lens system 200 including a focus lens group and a diaphragm S, and a negative refractive power disposed on the image side thereof. A tilt lens group 290 is formed. In a normal use state where tilting is not performed, the main optical axis a1 of the master lens system 200 and the optical axis a2 of the tilt lens group 290 coincide with each other to form a coaxial optical system, and the main optical axis a1 is formed of an image sensor or a film. It is orthogonal to the imaging surface 3 at its approximate center. The tilt lens group 290 at this time is indicated by a broken line. The image plane by the master lens system 200 of the subject plane NO at a short distance orthogonal to the main optical axis a1 is indicated by a broken line NF, and if there is no tilt lens group 290, a real image is formed at this position NF. The tilt lens group 290 disposed between the master lens system 200 and the image plane NF takes the plane NF as an input and forms an enlarged output image on the imaging plane 3.

  Next, the effect when the optical axis a2 of the tilt lens group 290 is inclined by θ1 will be described. When tilting so that the main plane of the tilt lens group and the imaging plane 3 intersect at the intersection line is1, the input plane conjugate with the imaging plane 3 as an output is tilted so as to coincide with the intersection line is1 according to Shine-Pruff's law. The plane TF forms an angle with the imaging surface 3 and θ2. Next, considering the imaging relationship of the master lens system 200, the image plane as an output is inclined by θ2, and becomes a plane TF. Therefore, the main plane of the master lens system 200 and the image plane TF intersect at an intersection line is2. According to Shine-Pluff's law, the subject plane that is the input at this time must be a plane TO that has the intersection line is2 and is inclined by θ3. Therefore, when the tilt lens group 290 is tilted counterclockwise by θ1 on the paper surface in FIG. 1, the subject plane in focus becomes the plane TO tilted by θ3 clockwise.

  Next, the principle that AF and AE work normally even during tilting, which is the main object of the present invention, will be described. The main reason why the conventional single lens reflex tilt lens is manual focus instead of AF is that the symmetry of the subject information incident on the AF sensor is lost optically when tilting, and so-called phase difference detection AF malfunctions. It is for inviting. The main factors that cause the symmetry of subject information incident on the AF sensor to be lost are considered to be parallel decentering of the exit pupil due to shift tilt and asymmetry of the aperture efficiency due to tilting of the thick photographing lens. The same can be said about the malfunction of AE, and the light flux emitted from the photographing lens determined by the open F number and the aperture efficiency is at the same position as the diffusion by the focusing screen at the position equivalent to the imaging surface. The light beam is bent by the Fresnel lens and reaches the photometric element located near the eyepiece. However, the tilt of the light beam from the lens that is incident on the Fresnel lens changes due to shifting and tilting operations. In this case, it is considered that the AE malfunctions because the brightness reaching the photometric element changes even though the image plane illuminance does not change. In the present invention, first, the shift tilt which causes the greatest malfunction of AF and AE is not adopted, but it is left to the processing function of the retouching software, and then the focus lens group and the aperture which cause the asymmetry of the light bundle emitted from the lens Is always placed on the main optical axis, and the fixed aperture that causes aperture efficiency is also not displaced from the main optical axis, so that the beam bundle reaching the AF sensor and the photometric element is symmetrical even when tilt tilt is performed. The effect is hardly lost and malfunction is hardly caused.

  Also, considering the difficulty in constructing a mechanical linkage mechanism with the body of a single-lens reflex camera, with regard to AF, even a single-lens reflex camera system having a mechanism that drives a focus lens group with a motor in the body In recent years, the focus lens group has been driven by an in-lens motor, and it is relatively easy to drive AF without using an in-body motor. Driving can be realized. However, with regard to the drive of the aperture, there are few that employ an electrically interlocked system of the in-lens motor, and an instantaneous automatic aperture is realized by mechanically interlocking the lever on the body side and the lens side. There are many. In this case, with the tilt lens that tilts the entire photographic lens, the diaphragm interlocking lever that is directly connected to the lens-side diaphragm device falls down, making it extremely difficult to convey the movement correctly mechanically. For this reason, it is considered that the conventional interchangeable lens with a tilt tilt function adopts a preset diaphragm method in which the user manually performs the narrowing and opening operations. In the present invention, since the focus lens group and the diaphragm are always on the main optical axis, the prior art diaphragm interlocking mechanism can be adopted, and it is only possible to solve both the tilt mechanism of the tilt lens group 290 and the diaphragm interlocking mechanism. It remains as a major issue.

  The malfunction of AF and AE has been described on the premise of a single-lens reflex digital camera and a film camera. However, in an imaging apparatus such as a compact digital camera that also serves as an AF and AE sensor, it is more optical, Mechanical constraints are reduced, and problems for avoiding malfunctions are reduced.

  The most distinctive feature of the tilt lens system of the present invention is that it becomes an extremely decentered optical system at the time of tilting, so that aberration correction at the time of tilting is performed compared to a conventional tilt lens system that tilts with a coaxial optical system. Maintenance is a major issue. Even with the conventional tilt lens system, it will be used up to the outside of the normal image circle at the time of tilting compared to the normal use state, so it is necessary to sufficiently correct the aberration up to the image circle larger than the size of the imaging surface, It does not mean that there is no image quality degradation at the time of tilting. In the case of the configuration of the tilt lens system 2 of the present invention shown in FIG. 1, since the angle of view at which the master lens system 200 looks at the subject hardly changes even during tilting, the master lens system 200 has no need to forcibly widen the image circle. Good aberration correction and downsizing of the front lens diameter are possible.

  Conditional expression (1) is for effectively exerting the tilt effect described with reference to FIG. 1. If the tilt angle θ1 is increased below the lower limit value, a sufficient subject inclination θ3 cannot be obtained, and θ3. Is increased, the path of the light beam passing through each surface of the tilt lens group 290 is completely different from the state of the coaxial optical system, and it becomes difficult to maintain the balance of aberration correction. If the upper limit is exceeded, a large subject tilt angle θ3 can be obtained with a small tilt angle θ1, but it is difficult to brighten the F-number of the entire system. That is, since the tilt lens system of the present invention has a refractive power arrangement such that a rear conversion lens is added to a master lens system in which aberrations are well corrected, the F number unique to the master lens system 200 is set like a rear conversion lens. The tilt lens group 290 is dark, and the F number of the entire system is determined. In order to have practical merchandise, the F number of the entire system is preferably about F4, for example. If βt = 1.4, the inherent F number of the master lens system is F2.8, and the design can be advanced by combining a rear conversion lens with a magnification of 1.4 times with a macro lens of F2.8. However, if βt = 1.7, the master lens system requires F2.35, and an extremely bright light beam enters the tilt lens system. However, it is known that even with a rear conversion lens, the higher the magnification is, the more difficult it is to correct the aberration. Further, when trying to establish the balance of the aberration correction at the time of tilting, the solution is lost.

  Conditional expression (2) indicates that when the tilt lens system 2 is used as an interchangeable lens of a single-lens reflex camera, a mechanical structure that tilts the tilt lens group 290 with a sufficient tilt angle in an arbitrary azimuth angle direction, and aberration during tilting This is related to the balance of correction. In Patent Documents 2 and 3, it is suggested that the position of the rotation center of the tilt lens group should be determined on the condition that the center image does not move. In the present invention, however, the tilt variation and the tilt mechanism are determined. I think that it should be decided from the condition of securing the space for incorporation into the interchangeable lens. If the upper limit is exceeded, the center of rotation and the flange surface of the interchangeable lens will approach or overlap, making it difficult to construct a mechanism that tilts to an arbitrary azimuth angle. Below the lower limit, an astigmatic difference between meridional and sagittal tends to occur on the plus side and minus side of the image height.

In the tilt lens system according to an embodiment of the present invention, the tilt lens group includes a positive lens group, a negative lens group, a negative lens group, and a positive lens group in order from the object side. It is desirable to satisfy conditional expressions (3) and (4).
(3) 1.25 <| ft1 / ft2 | <1.9
(4) 0.3 <| ft3 / ft4 | <0.85
However,
fti: The focal length of the i-th lens unit from the object side of the tilt lens unit.

  As an example in which this embodiment is embodied, for example, the configuration shown in FIG. 2 is conceivable. The tilt lens group 290 includes, in order from the object side, a positive lens group 250, a negative lens group 260, a negative lens group 270, and a positive lens. The refractive power arrangement of the group 280 is adopted.

  With such a configuration, the tilt lens group 290 is configured like a teleconversion lens added to the object side of the master lens, and aberration correction can be sufficiently performed by the tilt lens group 290 alone. Note that when the tilt lens group 290 is configured as shown in FIG. 2, if the lower limit value of the conditional expression (2) is not reached, the rotational center moves away from the negative lens group 270 and the positive lens group 280, and the image plane characteristics are improved. The two lens groups 270 and 280 that are deeply involved are greatly swung, and the astigmatic difference between the meridional and the sagittal tends to occur between the plus side and the minus side of the image height.

  Conditional expression (3) relates to coma at the center of the screen at the time of tilting. The most image side surface of the positive lens group 250 and the object side surface of the negative lens group 260 are spherical aberrations in the case of a coaxial optical system. However, if the tilt lens group 290 is rotated counterclockwise on the paper surface as shown in FIG. 2, the upper ray side of the light bundle toward the center of the screen passes through the two surfaces. The light beam is strongly bent downward on the lens 250 side and strongly bent upward so as to cancel it on the negative lens 260 side. If the lower limit value of conditional expression (3) is not reached, the downward coma aberration will increase, and if it exceeds the upper limit value, the upward coma aberration will be significant, and both will be difficult to correct.

  Conditional expression (4) relates to image plane characteristics with respect to a tilted subject at the time of tilting. If the range defined by conditional expression (4) is not satisfied, the tilt lens group 290 is tilted counterclockwise on the paper as shown in FIG. In this case, the astigmatic difference between the meridional and sagittal becomes significant at the negative image height, and correction becomes difficult.

In the tilt lens system according to an embodiment of the present invention, the positive lens group closest to the object side of the tilt lens group includes, in order from the object side, a negative lens having a strong concave surface facing the image side, and strong against the object side. A positive lens having a convex surface is disposed, and the curvatures of the opposing surfaces of the two lenses are very close or the two lenses are cemented, and the following conditional expression (5) is satisfied. It is desirable.
(5) (nt11-nt12)> 0.17
However,
nt11: Refractive index of the negative lens in the positive lens group nt12: Refractive index of the positive lens in the positive lens group.

  As a result, good image surface characteristics can be realized even during tilting.

  Conditional expression (5) relates to the balance of the Petzval sum of the master lens system 200 and the tilt lens group 290 as well as the correction of the image plane by setting the Petzval sum to an appropriate value. If only the Petzval sum of the entire system is set to an appropriate value, there is no problem in the case of a coaxial optical system even if the master lens system 200 is larger on the plus side and the tilt lens group 290 is larger on the minus side. However, if the tilt lens group 290 is tilted with a large negative Petzval sum, the characteristic of the image plane correction inherent to the tilt lens group 290 deteriorates, resulting in an astigmatic difference during tilting. Accordingly, even if the lens system is not an independent lens system as in the case of the rear conversion lens, the positive lens group closest to the object side of the tilt lens group 290 has a strong concave surface facing the image side in order from the object side. The negative lens and a positive lens having a strong convex surface facing the object side, and the difference in refractive index between these two lenses must be taken large so that the Petzval sum becomes an appropriate value.

In the tilt lens system according to an embodiment of the present invention, the second negative lens group from the object side of the tilt lens group includes, in order from the object side, a positive lens having a strong convex surface facing the image side, and the object side. A negative lens with a strong concave surface facing each other, and the curvatures of the opposing surfaces of the two lenses are very close, or the two lenses are cemented, and the following conditional expression (6) is satisfied It is desirable to do.
(6) (nt21-nt22) <-0.1
However,
nt21: Refractive index of the positive lens in the negative lens group nt22: Refractive index of the negative lens in the negative lens group.

  As a result, coma aberration generated at the center of the screen during tilting can be suppressed, and the tilt angle can be increased while maintaining good aberration correction.

  In order to suppress the coma aberration that occurs at the center of the screen during tilting, it is necessary to make the most object side surface of the second negative lens unit from the object side of the tilt lens unit a convex surface having a weak curvature. Satisfying the expression (6), it is necessary to share negative refractive power between the image side surface of the positive lens and the object side surface of the negative lens (a cemented surface when two lenses are cemented).

In the tilt lens system according to an embodiment of the present invention, the positive lens group closest to the object side of the tilt lens group, in order from the object side, a negative lens with a strong concave surface facing the image side, a biconvex lens, Negative lenses with concave surfaces facing the object side are arranged, and the curvatures of the surfaces facing each other of the three lenses are very close or the three lenses are cemented, and the following conditional expression (5) And it is desirable to satisfy (7).
(5) (nt11-nt12)> 0.17
(7) (nt12-nt13) <-0.07
However,
nt11: Refractive index of the object side negative lens in the positive lens group nt12: Refractive index of the biconvex lens in the positive lens group nt13: Refractive index of the image side negative lens in the positive lens group.

  Accordingly, the coma aberration generated at the center of the screen at the time of tilting can be corrected more favorably, and even at the time of tilting, the coma aberration can be corrected as well as the spherical aberration at the time of the coaxial optical system.

  By satisfying conditional expression (7), the image side surface of the biconvex lens of the positive lens unit closest to the object side of the tilt lens unit and the object side surface of the image side negative lens (if the positive lens unit is a triplet cemented lens, the image side surface) The negative coma is given to the side cemented surface, and the downward coma aberration generated on the surface emitting the positive lens group is reduced to the front side (the image side surface of the biconvex lens and the object side surface of the image side negative lens ( When the positive lens group is a three-lens cemented lens, the above effect can be produced by generating an upward coma aberration on the image side cemented surface)) and canceling it.

In the tilt lens system according to an embodiment of the present invention, the positive lens group closest to the object side of the tilt lens group, in order from the object side, a negative lens with a strong concave surface facing the image side, a biconvex lens, Negative lenses with concave surfaces facing the object side are arranged, and the curvatures of the surfaces facing each other of the three lenses are very close or the three lenses are cemented, and the following conditional expression (5) And it is desirable to satisfy (8).
(5) (nt11-nt12)> 0.17
(8) (nt12-nt13)> 0.02
However,
nt11: Refractive index of the object side negative lens in the positive lens group nt12: Refractive index of the biconvex lens in the positive lens group nt13: Refractive index of the image side negative lens in the positive lens group.

  Accordingly, the coma aberration generated at the center of the screen at the time of tilting can be corrected more favorably, and even at the time of tilting, the coma aberration can be corrected as well as the spherical aberration at the time of the coaxial optical system.

  By satisfying conditional expression (8), the image side surface of the biconvex lens of the positive lens group closest to the object side of the tilt lens group and the object side surface of the image side negative lens (if the positive lens group is a triplet cemented lens, the image side surface) The above-mentioned effect can be produced by imparting positive refractive power to the side joining surface) and dispersing the positive refractive power to the subsequent exit surface.

  In the tilt lens system according to an embodiment of the present invention, it is desirable to dispose a fixed lens group that is fixed with respect to the imaging surface during focusing, between the focus lens group and the tilt lens group.

  A fixed lens group is always disposed between the focus lens group and the tilt lens group, and changes in the light path due to focusing can be applied to suppress variations in various aberrations. That is, it is possible to solve the variation in the distance of aberration due to focusing. The fixed lens group has a function of correcting short-distance aberrations regardless of magnification or reduction.

In the tilt lens system according to an embodiment of the present invention, the fixed lens group includes a cemented lens of a positive lens and a negative lens, which are sequentially located from the object side, and satisfies the following conditional expression (9). It is desirable.
(9) 0.5 <βf <1.2
However,
βf: The lateral magnification of the fixed lens group.

  If the lower limit value of conditional expression (9) is not reached, various aberrations generated from the focus lens group are reduced, which is advantageous for correction of aberrations in the entire system. However, the total length and the amount of feeding at the time of focusing become too large. It becomes difficult. Beyond the upper limit, it is advantageous for downsizing, but the various aberrations inherent in the focus lens group are expanded by the fixed lens group and further expanded by the tilt lens group, so that desired imaging performance can be achieved. become unable.

In the tilt lens system according to an embodiment of the present invention, the focus lens group includes, in order from the object side, a negative lens having a strong concave surface facing the image side, a biconvex lens, a diaphragm, and a concave surface on the object side. It is desirable that the negative lens directed, the biconvex lens, and the positive lens having a strong convex surface on the image side are arranged, and the following conditional expression (10) is satisfied.
(10) 1.25 <h2 / h1 <1.6
However,
h1: Paraxial ray height incident in parallel to the optical axis h2: Paraxial ray height when the second lens is emitted with respect to h1.

  As a result, it is possible to achieve both the securing of a long back focus sufficient to dispose the tilt lens group on the image side and the suppression of aberration distance fluctuations by a relative effect with the fixed lens group.

  In this embodiment, a more specific configuration of the focus lens group is determined. In many cases, a gauss type or a modified type of the macro lens is adopted. However, in the tilt lens system of the present invention, the focus lens group is a retrofocus type in order to arrange a large number of tilt lens groups on the image side. Need to increase back focus. Since a large number of lenses are used for the tilt lens group and two lenses are arranged for the fixed lens group, the focus lens group uses a simplified retrofocus lens with as few lenses as possible to absorb and reflect light. It is important to suppress.

  If the lower limit value of conditional expression (10) is not reached, sufficient back focus as the focus lens group cannot be secured, and it becomes difficult to dispose the tilt lens group. If the upper limit is exceeded, the Petzval sum tends to increase on the negative side, making it difficult to correct field curvature.

  Next, specific embodiments embodying the tilt lens system of the present invention will be described.

  FIG. 2 shows the lens configuration of the first embodiment 2A of the tilt lens system of the present invention. The tilt lens system 2A is, in order from the object side, a master lens system 200, and a tilt lens that has a negative refractive power and can tilt the optical axis a2 with respect to the optical axis (main optical axis) a1 of the master lens system 200. A group 290 is arranged. The tilt lens group 290 forms a coaxial optical system in which the optical axis a2 coincides with the optical axis a1 of the master lens system 200 when the optical axis a2 is not inclined. The master lens system 200 includes a focus lens group 210 and a fixed lens group 220 arranged in order from the object side.

  The focus lens group 210 includes, in order from the object side, a negative meniscus lens 211 having a strong concave surface facing the image side, a biconvex lens 212, an aperture stop S, a biconcave lens 213 having a concave surface facing the object side, and a biconvex lens 214. A biconvex lens 215 having a strong convex surface facing the lens and the image side is arranged. The fixed lens group 220 includes a cemented positive lens composed of a biconvex lens 221 and a biconcave lens 222, which are sequentially positioned from the object side.

  The tilt lens group 290 includes, in order from the object side, a positive lens group 250 including a cemented positive lens of a negative meniscus lens 251 having a strong concave surface facing the image side and a biconvex lens 252 having a strong convex surface facing the object side. A negative lens group 260 made up of, a negative lens group 270 made up of a biconcave lens, and a positive lens group 280 made up of a biconvex lens.

  Table 1 shows that in the coaxial optical system of Numerical Example 1 in which specific numerical values are applied to the first embodiment 1A, that is, the tilt angle θ1 of the optical axis a2 of the tilt lens group 290 with respect to the main optical axis a1 = Data of each optical element at 0, that is, a radius of curvature r, a surface interval d, a refractive index nd, and an Abbe number νd are shown. The surface number i indicates the i-th surface from the object side, the surface interval d indicates the axial top surface interval between the i-th surface and the (i + 1) -th surface, and the refractive index nd. And Abbe number νd are for the d-line (λ (wavelength) = 587.6 nm (nanometer)), respectively.

  Table 2 shows the focal length, F-number, field angle (2ω), maximum image height, lateral magnification, distance from the object to the first surface, and variable distance (d10 = focus lens group 210 and fixed lens) in Numerical Example 1. Interval between groups 220).

  Table 3 shows the optimum object inclination angles θ3 and d10 when θ1 is 13 degrees in Numerical Example 1.

  FIG. 3 (lateral magnification = 0), FIG. 4 (lateral magnification = −0.1), and FIG. 5 (lateral magnification) the spherical aberration, field curvature, and distortion at each magnification when θ1 = 0 in Numerical Example 1. = -0.5). Further, when d10 = 3.453, the lateral aberration curves of meridional and sagittal at θ1 = 0 and θ1 = 13 degrees and θ3 = 39 degrees are shown in FIG. 6 (θ1 = 0) and FIG. 7 (θ1 = 13 degrees and θ3). = 39 degrees).

  In each aberration diagram, the solid line in the spherical aberration curve and the lateral aberration curve is the d line, the broken line is the g line (λ = 435.8 nm), and the alternate long and short dash line is the value with respect to the C line (λ = 656.3 nm). The solid line in the astigmatism curve indicates the sagittal image, and the broken line indicates the meridional image surface.

  FIG. 8 shows the lens configuration of the second embodiment 2B of the tilt lens system of the present invention. The tilt lens system 2B is, in order from the object side, a master lens system 200 and a tilt lens that has a negative refractive power and can tilt the optical axis a2 with respect to the optical axis (main optical axis) a1 of the master lens system 200. A group 290 is arranged. The tilt lens group 290 forms a coaxial optical system in which the optical axis a2 coincides with the optical axis a1 of the master lens system 200 when the optical axis a2 is not inclined. The master lens system 200 includes a focus lens group 210 and a fixed lens group 220 arranged in order from the object side.

  The focus lens group 210 includes, in order from the object side, a negative meniscus lens 211 having a strong concave surface facing the image side, a biconvex lens 212, an aperture stop S, a biconcave lens 213 having a concave surface facing the object side, and a biconvex lens 214. A biconvex lens 215 having a strong convex surface facing the lens and the image side is arranged. The fixed lens group 220 is composed of a cemented negative lens of a biconvex lens 221 and a biconcave lens 222, which are located in order from the object side.

  The tilt lens group 290 includes, in order from the object side, a positive lens group 250 including a cemented positive lens of a negative meniscus lens 251 having a strong concave surface facing the image side and a biconvex lens 252 having a strong convex surface facing the object side. A negative lens group 260 composed of a cemented negative lens of a biconvex lens 261 with a strong convex surface facing the object and a biconcave lens 262 with a strong concave surface facing the object side, a negative lens group 270 composed of a biconcave lens, and a strong convex surface directed toward the object side A positive lens group 280 made up of positive meniscus lenses is arranged.

  Table 4 shows that in the coaxial optical system of Numerical Example 2 in which specific numerical values are applied to the second embodiment 1B, that is, the tilt angle θ1 of the optical axis a2 of the tilt lens group 290 with respect to the main optical axis a1 = Data of each optical element at 0, that is, a radius of curvature r, a surface interval d, a refractive index nd, and an Abbe number νd are shown. The surface number i indicates the i-th surface from the object side, the surface interval d indicates the axial top surface interval between the i-th surface and the (i + 1) -th surface, and the refractive index nd. And Abbe number νd are for the d line.

  Table 5 shows the focal length, F-number, field angle (2ω), maximum image height, lateral magnification, distance from the object to the first surface, and variable distance (d10 = focus lens group 210 and fixed lens) in Numerical Example 2. Interval between groups 220).

  Table 6 shows the optimum object inclination angles θ3 and d10 when θ1 is 15 degrees in Numerical Example 2.

  FIG. 9 (lateral magnification = 0), FIG. 10 (lateral magnification = −0.1), and FIG. 11 (lateral magnification) for spherical aberration, field curvature, and distortion at each magnification when θ1 = 0 in Numerical Example 2. = -0.5). Further, when d10 = 7.448, the meridional and sagittal lateral aberration curves at θ1 = 0 and θ1 = 15 degrees and θ3 = 49 degrees are shown in FIG. 12 (θ1 = 0) and FIG. 13 (θ1 = 15 degrees and θ3). = 49 degrees).

  In each aberration diagram, the solid line in the spherical aberration curve and the lateral aberration curve is the d line, the broken line is the g line, the alternate long and short dash line is the value for the C line, the solid line in the astigmatism curve is the sagittal, and the broken line is the meridional image. Show the surface.

  In the numerical example 1, as shown in FIG. 7, good aberration correction was realized at θ1 = 13 degrees, but the meridional lateral aberration in FIG. 7 and the aberration curve indicated by the arrow at Y = 0 show downward coma. Is seen. This coma aberration increases rapidly when θ1 is further tilted, resulting in performance that cannot be used as a macro lens. Therefore, there remains a problem that the subject tilt angle cannot be further increased. The cause of this coma aberration is that the light beam corresponding to this aberration is strongly bent downward on the 16th surface (the image side surface of the positive lens group 250) and then upward on the 17th surface (the object side surface of the negative lens group 260). This is probably because the influence of 16 faces remains stronger as the size increases. In the numerical value example 2, the positive lens 252 in FIG. 2 is divided into two to obtain the positive lens 252 and the positive lens 261 in FIG. Then, the positive lens 261 is joined to the negative lens group 260 side in FIG. 2 to reduce the curvature of the two surfaces where the coma aberration occurs, that is, the surface closest to the image side of the positive lens group 250. The most object-side surface is changed from a concave surface to a convex surface having a weak curvature, and the deviation angle of the light beam corresponding to the coma aberration in the two surfaces is reduced, so that the aberration deterioration is reduced to a tilt angle θ1 larger than that in Numerical Example 1. As improved. In order to make the most object side surface of the negative lens group 260 a convex surface having a weak curvature, it is necessary to satisfy the conditional expression (6) and to share negative refractive power to the cemented surface in the negative lens group 260.

  FIG. 14 shows the lens configuration of the third embodiment 2C of the tilt lens system of the present invention. The tilt lens system 2C is, in order from the object side, a master lens system 200, and a tilt lens that has a negative refractive power and can tilt the optical axis a2 with respect to the optical axis (main optical axis) a1 of the master lens system 200. A group 290 is arranged. The tilt lens group 290 forms a coaxial optical system in which the optical axis a2 coincides with the optical axis a1 of the master lens system 200 when the optical axis a2 is not inclined. The master lens system 200 includes a focus lens group 210 and a fixed lens group 220 arranged in order from the object side.

  The focus lens group 210 includes, in order from the object side, a negative meniscus lens 211 having a strong concave surface facing the image side, a biconvex lens 212, an aperture stop S, a biconcave lens 213 having a concave surface facing the object side, and a biconvex lens 214. A biconvex lens 215 having a strong convex surface facing the lens and the image side is arranged. The fixed lens group 220 is composed of a cemented negative lens of a biconvex lens 221 and a biconcave lens 222, which are located in order from the object side.

  The tilt lens group 290 includes, in order from the object side, a positive cemented three-lens lens including a negative meniscus lens 251 having a strong concave surface facing the image side, a biconvex lens 252 and a negative meniscus lens 253 having a concave surface facing the object side. The lens group 250, a negative lens group 260 composed of a cemented negative lens of a biconvex lens 261 with a strong convex surface facing the image side and a biconcave lens 262 with a strong concave surface facing the object side, a negative lens group 270 composed of a biconcave lens, the object side A positive lens group 280 made up of positive meniscus lenses having a strong convex surface facing each other is arranged.

  Table 7 shows the coaxial optical system of Numerical Example 3 in which specific numerical values are applied to the third embodiment 1C, that is, the tilt angle θ1 of the optical axis a2 of the tilt lens group 290 with respect to the main optical axis a1 = Data of each optical element at 0, that is, a radius of curvature r, a surface interval d, a refractive index nd, and an Abbe number νd are shown. The surface number i indicates the i-th surface from the object side, the surface interval d indicates the axial top surface interval between the i-th surface and the (i + 1) -th surface, and the refractive index nd. And Abbe number νd are for the d line.

  Table 8 shows the focal length, F number, field angle (2ω), maximum image height, lateral magnification, distance from the object to the first surface, and variable distance (d10 = focus lens group 210 and fixed lens) in Numerical Example 3. Interval between groups 220).

  Table 9 shows the optimum object inclination angles θ3 and d10 when θ1 is 15 degrees in Numerical Example 3.

  FIG. 15 (lateral magnification = 0), FIG. 16 (lateral magnification = −0.1), and FIG. 17 (lateral magnification) the spherical aberration, field curvature, and distortion at each magnification when θ1 = 0 in Numerical Example 3. = -0.5). Further, when d10 = 7.512, the meridional and sagittal lateral aberration curves at θ1 = 0 and θ1 = 15 degrees and θ3 = 49 degrees are shown in FIG. 18 (θ1 = 0) and FIG. 19 (θ1 = 15 degrees and θ3). = 49 degrees).

  In each aberration diagram, the solid line in the spherical aberration curve and the lateral aberration curve is the d line, the broken line is the g line, the alternate long and short dash line is the value for the C line, the solid line in the astigmatism curve is the sagittal, and the broken line is the meridional image. Show the surface.

  FIG. 20 shows the lens configuration of the fourth embodiment 2D of the tilt lens system of the present invention. The tilt lens system 2D is, in order from the object side, a master lens system 200 and a tilt lens that has a negative refractive power and can tilt the optical axis a2 with respect to the optical axis (main optical axis) a1 of the master lens system 200. A group 290 is arranged. The tilt lens group 290 forms a coaxial optical system in which the optical axis a2 coincides with the optical axis a1 of the master lens system 200 when the optical axis a2 is not inclined. The master lens system 200 includes a focus lens group 210 and a fixed lens group 220 arranged in order from the object side.

  The focus lens group 210 includes, in order from the object side, a negative meniscus lens 211 having a strong concave surface facing the image side, a biconvex lens 212, an aperture stop S, a biconcave lens 213 having a concave surface facing the object side, and a biconvex lens 214. A biconvex lens 215 having a strong convex surface facing the lens and the image side is arranged. The fixed lens group 220 is composed of a cemented negative lens of a biconvex lens 221 and a biconcave lens 222, which are located in order from the object side.

  The tilt lens group 290 includes, in order from the object side, a positive cemented three-lens lens including a negative meniscus lens 251 having a strong concave surface facing the image side, a biconvex lens 252 and a negative meniscus lens 253 having a concave surface facing the object side. The lens group 250, a negative lens group 260 composed of a cemented negative lens of a biconvex lens 261 with a strong convex surface facing the image side and a biconcave lens 262 with a strong concave surface facing the object side, a negative lens group 270 composed of a biconcave lens, the object side A positive lens group 280 made up of positive meniscus lenses having a strong convex surface facing each other is arranged.

  Table 10 shows that in the coaxial optical system of Numerical Example 4 in which specific numerical values are applied to the fourth embodiment 1D, that is, the tilt angle θ1 of the optical axis a2 of the tilt lens group 290 with respect to the main optical axis a1 = Data of each optical element at 0, that is, a radius of curvature r, a surface interval d, a refractive index nd, and an Abbe number νd are shown. The surface number i indicates the i-th surface from the object side, the surface interval d indicates the axial top surface interval between the i-th surface and the (i + 1) -th surface, and the refractive index nd. And Abbe number νd are for the d line.

  Table 11 shows the focal length, F-number, field angle (2ω), maximum image height, lateral magnification, distance from the object to the first surface, and variable distance (d10 = focus lens group 210 and fixed lens) in Numerical Example 4. Interval between groups 220).

  Table 12 shows the optimum object inclination angles θ3 and d10 when θ1 is 15 degrees in Numerical Example 4.

  FIG. 21 (lateral magnification = 0), FIG. 22 (lateral magnification = −0.1), and FIG. 23 (lateral magnification) show the spherical aberration, field curvature, and distortion at each magnification when θ1 = 0 in Numerical Example 4. = -0.5). Further, when d10 = 7.510, the meridional and sagittal lateral aberration curves at θ1 = 0 and θ1 = 15 degrees and θ3 = 48 degrees are shown in FIGS. 24 (θ1 = 0) and 25 (θ1 = 15 degrees and θ3). = 48 degrees).

  In each aberration diagram, the solid line in the spherical aberration curve and the lateral aberration curve is the d line, the broken line is the g line, the alternate long and short dash line is the value for the C line, the solid line in the astigmatism curve is the sagittal, and the broken line is the meridional image. Show the surface.

  Next, features of the numerical example 3 and the numerical example 4 will be described. The improvement effect from Numerical Example 1 to Numerical Example 2 is obvious in the comparison between FIG. 7 and FIG. 13 as described above. However, when FIG. 12 and FIG. 13 are compared, the frame of the arrow portion in FIG. Aberrations are caused by tilting and the same image quality as without tilting cannot be expected. However, considering the use of the tilt macro lens system, it can be said that precise depiction is often required for photography of small articles, close-ups of flowers, and so on, so it can be said that further aberration correction is necessary even during tilting.

  Numerical Example 3 and Numerical Example 4 have similar structures, but the coma aberration is corrected by the opposite means. In both cases, the positive lens group 250 of the tilt lens group 290 is a three-piece cemented lens. First, numerical example 3 will be described. By satisfying conditional expression (7), negative refractive power is given to the second cemented surface of the positive lens group 250. An improvement effect is obtained by canceling out the downward coma aberration generated on the surface from which the positive lens group 250 exits by generating the upward coma aberration on the cementing surface in front of it. Next, numerical example 4 will be described. When the conditional expression (8) is satisfied, the second cemented surface of the positive lens group 250 has a positive refractive power as opposed to numerical example 3, and positive refraction is achieved. The generation of aberration is suppressed by dispersing the force on the joint surface and the subsequent exit surface.

  Table 13 shows values corresponding to the conditional expressions (1) to (10) of the numerical examples 1 to 4.

  Conventionally, tilt tilt tilt lenses cannot perform AF, and AE sometimes does not work correctly, and tilt tilt operations are complicated and difficult to use.

  The tilt lens system of the present invention shows the principle for AF and AE to work correctly during normal use and tilt-and-orientation, and can be used without any disadvantage as a normal lens. It is easy to control the depth of field, and it is possible to install an inexpensive tilt function by simply adding about 5 lenses and a simple tilt mechanism to a normal lens system. An easy tilt lens can be provided.

  Each of the above-described embodiments and numerical examples is an example for achieving the present invention. When applied to a single-lens reflex imaging apparatus, the master lens system 200 has a relatively long back focus, A lens system with a bright F number is suitable, and can be easily designed based on many photographing lens systems known in the prior art. Further, the master lens system 200 may be a zoom lens by moving a plurality of lens groups. In addition, it is considered that it is easy to create many variations in the tilt lens group 290 if it is designed so as to suppress aberration deterioration during tilt with reference to a single-lens reflex rear conversion lens. Furthermore, camera shake correction may be performed by moving a lens group other than the tilt lens group in a direction perpendicular to the optical axis.

  Next, the imaging apparatus of the present invention will be described.

An imaging apparatus according to the present invention includes a tilt lens system and an image sensor that converts an optical image formed by the tilt lens system into an electrical signal. The tilt lens system includes a focus lens group that is movable during focusing, and a diaphragm center. The tilt lens group that can tilt the optical axis with respect to the main optical axis shared by and has negative refractive power is disposed on the image side from the focus lens group and the stop, and the following conditional expressions (1) and ( Satisfy 2).
(1) 1.3 <βt <1.7
(2) 0 <P <H1
However,
βt: Lateral magnification of the tilt lens group when the optical axis is not tilted P: Distance from the most object side surface of the tilt lens group to the tilt center when the optical axis is tilted H1: From the most object side surface of the tilt lens group The distance to the first principal point.

  Therefore, in the present invention, by tilting only a part of the lens groups, it is possible to perform photographing that satisfies the Shine-Pruff's law, and not only in a normal use state but also when tilting, AF and AE. Can be used, and the tilt aori shooting operation can be easily performed.

  Next, an example of an embodiment embodying the imaging apparatus of the present invention will be shown. In this embodiment, the image pickup apparatus of the present invention is applied to a digital still camera, and FIG. 26 is a block diagram showing a configuration example of the digital still camera.

  The digital still camera 100 includes a lens block 10 having an imaging function, a camera signal processing unit 20 that performs signal processing such as analog-digital conversion of a captured image signal, and an image processing unit 30 that performs recording / reproduction processing of the image signal. An LCD (Liquid Crystal Display) 40 for displaying captured images, an R / W (reader / writer) 50 for writing / reading data to / from the memory card 51, and a CPU (Central Processing Unit) for controlling the entire apparatus. ) 60, an input unit 70 for an operation input by the user, and a lens drive control unit 80 for controlling driving of the lenses in the lens block 10.

  The lens block 10 includes an optical system including a tilt lens system 2 to which the present invention is applied, an imaging element 12 such as a CCD (Charge Coupled Device), and a CMOS (Complementary Metal-Oxide Semiconductor). The camera signal processing unit 20 performs signal processing such as conversion of an output signal from the image sensor 12 into a digital signal, noise removal, image quality correction, and conversion into a luminance / color difference signal. The image processing unit 30 performs compression encoding / decompression decoding processing of an image signal based on a predetermined image data format, conversion processing of data specifications such as resolution, and the like. As the tilt lens system 2, the above-described tilt lens systems 2A to 2D of the present invention and numerical examples 1 to 4 thereof can be used, and the tilt lens system 2 is implemented according to aspects other than the above-described embodiments and numerical examples. The tilt lens system of the present invention can also be used.

  The memory card 51 is composed of a detachable semiconductor memory. The reader / writer 50 writes the image data encoded by the image processing unit 30 to the memory card 51 and reads the image data recorded on the memory card 51. The CPU 60 is a control processing unit that controls each circuit block in the digital still camera, and controls each circuit block based on an instruction input signal or the like from the input unit 70.

  The input unit 70 includes, for example, a shutter release button for performing a shutter operation, a mode selection switch for selecting an operation mode, and the like, and outputs an instruction input signal corresponding to an operation by the user to the CPU 60. The lens drive control unit 80 controls a motor (not shown) that drives the lens in the tilt lens system 2 based on a control signal from the CPU 60.

  The operation of the digital still camera 100 will be briefly described below.

  In the shooting standby state, under the control of the CPU 60, the image signal captured by the lens block 10 is output to the LCD 40 via the camera signal processing unit 20 and displayed as a camera through image. When an instruction input signal for tilt tilt is input from the input unit 70, the CPU 60 outputs a control signal to the lens drive control unit 80, and the tilt lens system 2 is controlled based on the control of the lens drive control unit 80. The tilt lens group (290 in FIG. 2, etc.) is tilted (tilted).

  When a shutter (not shown) of the lens block 10 is released by an instruction input signal from the input unit 70, the captured image signal is output from the camera signal processing unit 20 to the image processing unit 30 and subjected to compression coding processing. Is converted into digital data of the data format. The converted data is output to the reader / writer 50 and written to the memory card 51.

  Note that focusing is performed by the lens drive control unit 80 in the tilt lens system 2 based on a control signal from the CPU 60, for example, when the shutter release button is half-pressed or when it is fully pressed for recording. This is done by moving the focus lens group.

  When reproducing the image data recorded on the memory card 51, predetermined image data is read from the memory card 51 by the reader / writer 50 in response to an operation by the input unit 70, and decompressed by the image processing unit 30. After the decoding process, the reproduced image signal is output to the LCD 40. As a result, a reproduced image is displayed.

  In the above-described embodiment, the case where the imaging apparatus of the present invention is applied to a digital still camera has been described. However, the imaging apparatus can also be applied to other imaging apparatuses such as a video camera.

  In addition, the shapes and numerical values of the respective parts shown in the embodiment and the numerical examples are only examples of specific embodiments for carrying out the present invention, and thus the technical scope of the present invention. Should not be interpreted in a limited way.

It is a figure explaining the principle of operation of an imaging device using the tilt lens system of the present invention. It is a figure which shows the lens structure of 1st Embodiment of this invention tilt lens system. FIG. 8 is a diagram showing various aberrations of Numerical Example 1 in which specific numerical values are applied to the first embodiment together with FIGS. 4 to 7, and this diagram shows spherical aberration and astigmatism at a lateral magnification of 0 in a coaxial optical system. It is a figure which shows an aberration and a distortion aberration. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.1 at the time of a coaxial optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.5 at the time of a coaxial optical system. It is a figure which shows the lateral aberration in the finite distance at the time of a coaxial optical system. It is a figure which shows a lateral aberration when a tilt lens group and an object surface are inclined in the same lens position as FIG. It is a figure which shows the lens structure of 2nd Embodiment of this invention tilt lens system. FIG. 14 is a diagram illustrating various aberrations of Numerical Example 2 in which specific numerical values are applied to the second embodiment together with FIGS. 10 to 13, and this diagram shows spherical aberration and astigmatism at a lateral magnification of 0 in a coaxial optical system. It is a figure which shows an aberration and a distortion aberration. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.1 at the time of a coaxial optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.5 at the time of a coaxial optical system. It is a figure which shows the lateral aberration in the finite distance at the time of a coaxial optical system. FIG. 13 is a diagram showing lateral aberration when the tilt lens group and the object surface are tilted at the same lens position as in FIG. 12. It is a figure which shows the lens structure of 3rd Embodiment of this invention tilt lens system. FIG. 20 is a diagram illustrating various aberrations of Numerical Example 3 in which specific numerical values are applied to the third embodiment together with FIGS. 16 to 19, and this diagram shows spherical aberration and astigmatism at a lateral magnification of 0 in a coaxial optical system. It is a figure which shows an aberration and a distortion aberration. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.1 at the time of a coaxial optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.5 at the time of a coaxial optical system. It is a figure which shows the lateral aberration in the finite distance at the time of a coaxial optical system. FIG. 20 is a diagram showing lateral aberration when the tilt lens group and the object surface are tilted at the same lens position as in FIG. 19. It is a figure which shows the lens structure of 4th Embodiment of the tilt lens system of this invention. FIG. 26 is a diagram illustrating various aberrations of Numerical Example 4 in which specific numerical values are applied to the fourth embodiment together with FIGS. 22 to 25, and this diagram shows spherical aberration and astigmatism at a lateral magnification of 0 in a coaxial optical system. It is a figure which shows an aberration and a distortion aberration. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.1 at the time of a coaxial optical system. It is a figure which shows the spherical aberration, astigmatism, and distortion aberration in lateral magnification -0.5 at the time of a coaxial optical system. It is a figure which shows the lateral aberration in the finite distance at the time of a coaxial optical system. FIG. 25 is a diagram illustrating lateral aberration when the tilt lens group and the object surface are tilted at the same lens position as in FIG. 24. 1 is a circuit block diagram of an embodiment in which the imaging apparatus of the present invention is applied to a digital still camera.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Imaging device, 2 ... Tilt lens system, 200 ... Master lens system, 290 ... Tilt lens group, 2A ... Tilt lens system, 200 ... Master lens system, 210 ... Focus lens group, S ... Diaphragm, 220 ... Fixed lens group 290 ... Tilt lens group, 250 ... Positive lens group, 260 ... Negative lens group, 270 ... Negative lens group, 280 ... Positive lens group, a1 ... Main optical axis, a2 ... Optical axis of tilt lens group, 100 ... Imaging device 2 ... Tilt lens system, 12 ... Image sensor

Claims (10)

A tilt lens group that can tilt the optical axis and has a negative refractive power with respect to the main optical axis shared by the focus lens group that is movable during focusing and the center of the aperture is located closer to the image side than the focus lens group and the aperture. ,
A tilt lens system satisfying the following conditional expressions (1) and (2):
(1) 1.3 <βt <1.7
(2) 0 <P <H1
However,
βt: Lateral magnification of the tilt lens group when the optical axis is not tilted P: Distance from the most object side surface of the tilt lens group to the tilt center when the optical axis is tilted H1: From the most object side surface of the tilt lens group The distance to the first principal point. The tilt lens group includes a positive lens group, a negative lens group, a negative lens group, and a positive lens group in order from the object side, and satisfies the following conditional expressions (3) and (4). The tilt lens system according to claim 1.
(3) 1.25 <| ft1 / ft2 | <1.9
(4) 0.3 <| ft3 / ft4 | <0.85
However,
fti: The focal length of the i-th lens unit from the object side of the tilt lens unit. The positive lens group closest to the object side of the tilt lens group includes, in order from the object side, a negative lens having a strong concave surface facing the image side and a positive lens having a strong convex surface facing the object side. 2. The tilt lens system according to claim 1, wherein the curvatures of the two lenses facing each other are extremely close to each other, or the two lenses are cemented, and the following conditional expression (5) is satisfied.
(5) (nt11-nt12)> 0.17
However,
nt11: Refractive index of the negative lens in the positive lens group nt12: Refractive index of the positive lens in the positive lens group. The second negative lens group from the object side of the tilt lens group is, in order from the object side, a positive lens having a strong convex surface directed to the image side and a negative lens having a strong concave surface directed to the object side. 2. The tilt lens system according to claim 1, wherein the curvatures of the opposed surfaces of the two lenses are very close or the two lenses are cemented, and the following conditional expression (6) is satisfied. .
(6) (nt21-nt22) <-0.1
However,
nt21: Refractive index of the positive lens in the negative lens group nt22: Refractive index of the negative lens in the negative lens group. The positive lens group closest to the object side of the tilt lens group is composed of, in order from the object side, a negative lens having a strong concave surface facing the image side, a biconvex lens, and a negative lens having a concave surface facing the object side. The curvatures of the surfaces of the three lenses facing each other are very close or the three lenses are cemented, and the following conditional expressions (5) and (7) are satisfied: The tilt lens system described in 1.
(5) (nt11-nt12)> 0.17
(7) (nt12-nt13) <-0.07
However,
nt11: Refractive index of the object side negative lens in the positive lens group nt12: Refractive index of the biconvex lens in the positive lens group nt13: Refractive index of the image side negative lens in the positive lens group. The positive lens group closest to the object side of the tilt lens group is composed of, in order from the object side, a negative lens having a strong concave surface facing the image side, a biconvex lens, and a negative lens having a concave surface facing the object side. The curvatures of the surfaces of the three lenses facing each other are extremely close to each other, or the three lenses are cemented, and the following conditional expressions (5) and (8) are satisfied: The tilt lens system described in 1.
(5) (nt11-nt12)> 0.17
(8) (nt12-nt13)> 0.02
However,
nt11: Refractive index of the object side negative lens in the positive lens group nt12: Refractive index of the biconvex lens in the positive lens group nt13: Refractive index of the image side negative lens in the positive lens group. The tilt lens system according to claim 1, wherein a fixed lens group that is fixed with respect to an imaging surface during focusing is disposed between the focus lens group and the tilt lens group. 8. The tilt lens system according to claim 7, wherein the fixed lens group includes a cemented lens of a positive lens and a negative lens, which are sequentially positioned from the object side, and satisfies the following conditional expression (9).
(9) 0.5 <βf <1.2
However,
βf: The lateral magnification of the fixed lens group. The focus lens group includes, in order from the object side, a negative lens having a strong concave surface facing the image side, a biconvex lens, a diaphragm, a negative lens having a concave surface facing the object side, a biconvex lens, and a strong convex surface facing the image side. 2. The tilt lens system according to claim 1, wherein a positive lens directed to the lens is arrayed and the following conditional expression (10) is satisfied:
(10) 1.25 <h2 / h1 <1.6
However,
h1: Paraxial ray height incident in parallel to the optical axis h2: Paraxial ray height when the second lens is emitted with respect to h1. An imaging apparatus comprising a tilt lens system and an image sensor that converts an optical image formed by the tilt lens system into an electrical signal,
The tilt lens system includes a tilt lens group that can tilt the optical axis and has a negative refractive power with respect to the main optical axis shared by the focus lens group that is movable during focusing and the center of the stop. Place it closer to the image side,
An image pickup apparatus satisfying the following conditional expressions (1) and (2):
(1) 1.3 <βt <1.7
(2) 0 <P <H1
However,
βt: Lateral magnification of the tilt lens group when the optical axis is not tilted P: Distance from the most object side surface of the tilt lens group to the tilt center when the optical axis is tilted H1: From the most object side surface of the tilt lens group The distance to the first principal point.

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